In general, a wiper is installed on a windshield of a vehicle in order to solve visibility obstacle occurring due to rainwater in case of rain. Intermittent speed control of the wiper is performed step by step according to the amount of falling raindrops. However, since such a wiper speed control system performs control through only several steps, the wiper cannot be driven at a speed desired by a driver according to the amount of rainwater.
In order to solve such a problem, a circuit board, on which a light source and a sensor, which is a light receiving element, are mounted, is provided to be inclined with respect to the surface of the windshield to minimize influence of light reflected from the surface of the windshield, and only an optical signal reflected from raindrops is received to increase rain sensing efficiency. That is, since light directly reflected from the windshield escapes from a light receiving range of the light receiving element to minimize the amount of light reflected from the windshield and received by the light receiving element and only the amount of light reflected from raindrops is received by the light receiving element, the circuit board including the light source and the light receiving element are provided to be inclined with respect to the surface of the windshield at a predetermined angle such that only diffused reflected signals from raindrops are sensed.
However, even in a product in which a circuit board including a light source and a light receiving element is provided to be inclined with respect to a windshield of a vehicle, since light emitted from the light source may be directly absorbed to the light receiving element, rain sensing efficiency is incomplete and insufficient. That is, light emitted from the light source is spread at a predetermined angle range. Even when the light source and the light receiving element are provided to be inclined with respect to the surface of the windshield, since some light other than light escaping from the windshield is directly irradiated toward the light receiving element, raindrop sensing efficiency may be slightly reduced due to indirect light delivered from the light source to the light receiving element and thus rain sensing efficiency may be incomplete and insufficient.
Even when peripheral interference light such as light emitted from headlights of adjacent vehicles is minimized, some interference light may not be blocked. In addition, a light-sensing rain sensor is very sensitive and may be influenced by a small amount of unblocked peripheral light. Therefore, high rain sensing effects cannot be obtained. In addition, in order to implement a structure for minimizing influence of peripheral light, the structure may become slightly complicated. Therefore, productivity may not be efficient and product costs may be increased.